A steam turbine plant includes steam generator, high pressure turbine, a plurality of low pressure turbines. The steam turbine plant further includes a plurality of steam condensers which condense steam from the plurality of low pressure turbines and a plurality of low pressure feedwater heaters which are provided within the steam condensers as the structural elements respectively. A feedwater heater which is provided within a steam condenser is also called as a neck heater, since the feedwater heater is installed at an upper (neck) portion of the steam condenser. The low pressure feedwater heaters constitute a plurality of feedwater heating lines which are arranged and connected in parallel. The steam turbine plant has a plurality of high pressure feedwater heaters which heat a feedwater from the low pressure feedwater heaters by steam bled from the high pressure turbine. Each of the steam condensers are connected to each of adjacent steam condensers by a connection shell. The steam condensers, the feedwater heating lines which are provided with the low pressure feedwater heaters arranged and connected in parallel, the high pressure feedwater heaters and steam generator are connected in series by feedwater line.
The low pressure feedwater heaters use bled steam from low pressure turbines as a heating source of the feedwater.
Generally, tiers of low pressure feedwater heaters arranged in series in the feedwater heating lines increase, the amount of heat exchanged in the low pressure feedwater heater also increases, which may contribute to high efficiency in view of thermal or plant efficiency. Moreover, when the low pressure feedwater heaters are installed inside of the steam condensers to save space of the steam turbine plant, it is desirable to reduce pressure drop of the steam discharged from the low pressure turbines and flowing around the low pressure feedwater heaters. For this reason, a neck heater type of structure is adopted for the steam condensers of conventional steam turbine plant. The neck heater type of structure is that the low pressure feedwater heaters are installed and arranged inside of the steam condensers at neck portions, which are a space above a portion where the steam discharged from the low pressure turbines condenses in the steam condensers.
Therefore, in conventional steam turbine plant, which includes n units of casings, n units of low pressure turbines and n units of steam condensers, constitute n pieces of the feedwater heating lines inserted in series to the feedwater line respectively. Each of the feedwater heating lines has a same number of the low pressure feedwater heaters, which are connected in series, inside of the steam condensers. The same numbers of the low pressure feedwater heaters are arranged in each of the steam condensers. Additionally, since each of the steam condensers are connected to the adjacent steam condenser by connection shell, differences of pressure distribution among the steam condensers are mitigated.
Nevertheless, since each of the low pressure feedwater heaters are connected with the bleeding lines, which extend from the casings of the low pressure turbines as a heating source, space of the neck portion of the steam condensers is relatively small. Especially, the bleeding lines have a large diameter for the low pressure feedwater heaters, which are provided at an upstream side of the feedwater heating lines, because the feedwater heaters at an upstream side of the feedwater heating lines employs the steam bled from a downstream side of the low pressure turbines as the heating source. This causes difficulty in planning such a steam turbine plant, especially in designing an arrangement of bleeding lines, feedwater heating lines or supports of these bleeding lines or low pressure feedwater heater at the neck portions. And it may result in necessity of further internal structure inside the steam condensers. This may cause necessity of enlarging space for the plant itself. And it may cause not only increase of costs but also pressure drop of the steam flowing inside of the steam condensers, which may effects reduction of the plant efficiency.
From a viewpoint of the feedwater, the feedwater line has feedwater heating lines whose number is the same as the steam condensers and which are arranged in parallel in conventional steam turbine plant. However, in order to avoid unbalance of the feedwater among the feedwater heating lines, it is desirable to provide less numbers of feedwater heating lines, which may contribute to increasing redundancies of controls of the steam turbine plant, especially for nuclear power plant.